Doesn't powertools or tweakUI have something similiar? Or I must be thinking of another tweak program. Anyway, what those program do is edit the registry for you, when you go directly into the registry, it can get quite messy if you do things wrong in there. Just an FYI.
I accomplish it by the first way: Open it, it doesn't open to the size I want, I resize it. I close it, I open it and it is now the size I want.